The neuropeptide and neurotransmitter profiles are being examined in rats treated with various neurotoxicants either neonatally or at adult stage. Neonatal treatment with chlordecone or monosodium glutamate (MSG) produces select regional changes in [Met5]-enkephalin and Beta-endorphin level in hypothalamo-pituitary axis in the adult. These results suggest that the hypothalamo-pituitary axis is very sensitive to the toxic insults. Chlordecone treatment to the adult rats also produces alterations in 5-HT and NA turnover rates on the brain which may be correlated with the changes in neuroendocrinological and behavioral changes. Lithium treatment increases substance P level in several brain regions which may be related to the change in pain threshold seen in lithium treated rats.